1. Field of the Invention
The present invention relates to a workpiece dividing method suitably applicable in the case of dividing a workpiece such as a semiconductor wafer to obtain a plurality of devices.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a workpiece such as a disk-shaped semiconductor wafer to thereby partition a plurality of rectangular device regions where a plurality of devices such as ICs, LSIs, liquid crystal drivers, and flash memories are respectively formed on the front side. After grinding the back side of the workpiece and next performing necessary processing such as polishing, the workpiece is cut along the streets to divide the device regions, thus obtaining the individual devices.
In general, the division of the workpiece is performed by using a cutting apparatus called a dicing saw having a cutting blade, wherein the cutting blade is rotated at a high speed and fed in the workpiece. In recent years, a laser processing method has also been adopted, wherein a laser beam is applied to the workpiece in the condition where the focal point of the laser beam is set inside a region of the workpiece to be divided. According to a workpiece dividing method using this laser processing method, a pulsed laser beam having a transmission wavelength to the workpiece is applied to the workpiece from one side thereof along the streets in the condition where the focal point of the pulsed laser beam is set inside the workpiece, thereby continuously forming a modified layer inside the workpiece along each street. Thereafter, an external force is applied to the workpiece along the streets where the modified layers are formed to reduce the strength, thereby breaking the workpiece along the streets. For example, this dividing method has an advantage such that the width of each street can be reduced (see Japanese Patent No. 3408805, for example).